Paris: French presidential frontrunner Emmanuel Macron filed a legal complaint Thursday after his far-right rival Marine Le Pen repeated online rumours that he had an offshore account in the Bahamas during one of the fiercest TV debates in the nation`s history.

The pro-EU centrist Macron and Le Pen clashed repeatedly over terrorism, the economy and Europe in Wednesday`s hot-tempered debate watched by some 16.5 million people.

"I hope that we will not find out that you have an offshore account in the Bahamas," Le Pen said during the ferocious confrontation that was her last chance to claw back the gap before Sunday`s run-off voter.

Macron described the suggestion as "defamation".

A source close to the case said the 39-year-old ex-economy minister`s complaint targeted "information that circulated Wednesday night on the internet".

Macron`s campaign team said the rumours began circulating two hours before the debate started.

Speaking on France Inter radio Thursday, the centrist, pro-EU candidate characterised the insinuations as "fake news and lies" from "sites, some of which were linked to Russian interests".

"We will not hesitate to prosecute for defamation anyone who repeats this false information," an aide to Macron said.

Former US president Barack Obama threw his support behind Macron, saying in a video the candidate "appeals to people`s hopes and not their fears."

Obama said Macron had "put forward a vision for the important role that France plays in Europe and around the world" and added "Vive la France!"

The candidates were back at each other`s throats the day after the debate in which Le Pen branded Macron "the candidate of the elite" while he called her "the high priestess of fear".

After the bruising confrontation, a snap poll by French broadcaster BFMTV found that 63 percent of viewers thought Macron was the "most convincing" of the two, broadly mirroring forecasts for the decisive election on Sunday.

"I succeeded in what I set out to do, annoy Mr Macron," she said on a campaign stop in the western town of Dol-de-Bretagne, where protesters threw eggs at her entourage, although she was not hit.

"I was the people`s representative who dared take a seat at the table reserved for the elites," Le Pen said.

Macron, who headed to the southwestern town of Albi to meet supporters, told France Inter radio: "You can`t choke off all of the lies but you can kill off some of them."

During the visit, the former economy minister was criticised by some 50 union activists who demanded the abolition of France`s controversial 2016 labour reforms.The aggressive and often unruly debate shocked many observers used to a more reserved tone in French political discourse.

"It is misleading to call that fist fight a debate," an editorial in the right-leaning Figaro newspaper said.

Le Monde said it had been "brutal" and "violent from start to finish".

A poll by Elabe for BFMTV showing that Macron had convinced 63 percent of viewers compared to 34 percent for Le Pen suggested she did little to win over new voters.

Macron would win around 60 percent to Le Pen`s 40 percent if the vote were held now, surveys suggest.

Le Pen tried to portray Macron as being soft on Islamic fundamentalism, playing to the concerns of many of her supporters after a string of terror attacks in France.

But Macron was in combative form throughout, repeatedly portraying Le Pen`s proposals as simplistic, defeatist or dangerous and targeting her proposals to withdraw France from the euro in particular.

Le Pen called the euro, shared by 19 countries in the European Union and blamed by some in France for a rise in prices, "the currency of bankers, it`s not the people`s currency".

In the first round of the election on April 23, Marine Le Pen finished second behind Macron with 21.3 percent after softening the FN`s image over the past six years -- but without fully removing doubt about the party`s core beliefs.

She sees her rise as the consequence of growing right-wing nationalism and a backlash against globalisation reflected in the election of Donald Trump in the United States and Britain`s shock vote to leave the European Union.

"I am the candidate of the people of France such as we love it, of the nation that protects jobs, security, our borders," she said.